Signficant progress has been made in the development of an LC-MS/MS assay that detects day time levels of N-acetyltryptamine and melatonin in human plasma. The assay used deuterated internal standards to monitor recovery and to provide a basis for quantitatin. Theprinciples of this assay provide the basis for a high-throughput automated method. Initial studies have established that N-acetyltryptamine is present in blood and that it exhibits significant variation amoung volunteers who have provided blood through the NIH Blood Bank Research Donor Program. Limited results precludes further comment.